Nonwoven webs or sheets such as those made of paper find extensive use in modern society in the context of household cleaning activity. Paper towels, for example, are a staple item of commerce which have long been used to wipe up liquid spills and to remove stains and/or soil from hard surfaces such as window glass, countertops, sinks, porcelain and metal fixtures, walls and the like, and from other surfaces such as carpeting or furniture. Similarly, nonwoven sheets have been employed extensively in the context of wipes for personal cleaning, such as toilet and facial tissue.
Paper towels products which are especially useful for household cleaning have attributes which include relatively low density, high bulk, acceptable softness, high absorbency for both aqueous and nonaqueous liquids and acceptable strength and integrity, especially when wet. Prior art towel products having such attributes, and processes for their preparation, have been disclosed, for example, U.S. Pat. No. 3,905,863, issued Sep. 16, 1975 to Ayers; U.S. Pat. No. 3,974,025, issued Aug. 10, 1976 to Ayers; U.S. Pat. No. 4,191,609, issued Mar. 4, 1980 to Trokhan; U.S. Pat. No. 4,440,597, issued Apr. 3, 1984 to Wells and Hensler; U.S. Pat. No. 4,529,840, issued Jul. 16, 1985 to Trokhan; and U.S. Pat. No. 4,637,859, issued Jan. 20, 1987 to Trokhan. Paper towels, such as those of the types described in the foregoing patents, are especially useful for absorbing and wiping up liquid spills from both hard surfaces and other surfaces such as furniture and carpets. Paper towel products, however, are also frequently used, generally in combination with liquid cleaning solutions or solvents, to remove soil or stains from surfaces to which such soil or stains may be especially securely affixed. Such soil or stains, for example, may include food material on stove, oven, or cooking utensil surfaces, soap scum found in bathtubs and sinks, food and beverage stains on kitchen counters, ink or crayon markings on walls and furniture, and the like. These prior art materials typically require the consumer to clean soils and stains using a separate cleaning solution and wiping article, which involves a level of inconvenience.
Paper products used as toilet tissue for anal cleaning are also essentially dry, low density tissue papers that rely exclusively on mechanical processes to remove fecal matter from the perianal skin. These conventional products are rubbed against the perianal skin, typically with a pressure of about 1 psi (7 kilopascals) and basically scrape or abrade the fecal matter from the skin. After the first few wipes, the upper portion of the soil layer is removed because the wiping process is able to overcome the soil--soil cohesive forces that exist within the fecal matter. A cleavage is thereby created in the soil layer itself with the upper portion of the fecal layer being removed and the lower portion of the soil remaining adhered to the perianal skin. Conventional toilet tissue products are absorbent and with each successive wipe the fecal matter becomes increasingly dehydrated, causing it to adhere more tenaciously to the perianal skin and hair and making its removal difficult in the extreme. Pressing the tissue forcefully against the perianal skin will remove more of the fecal matter but is intensely painful for people suffering from anal disorders and can excoriate even normal perianal skin, potentially causing irritation, inflammation, pain, bleeding, and infection.
To address the issue of convenience for wiping articles, pre-wetted wiping articles have been developed, particularly in the area of baby wipes. These pre-wetted wipes are generally kept in a dispenser and are typically soaked in a reservoir of a moistening solution. There is often a lack of consistency in terms of the moisture content of each of the wipes, with those initially used having less liquid than those used later and the wipes feel cold to the touch. Also, because the main purpose of such wipes is to clean, these wipes generally exhibit relatively poor post-cleaning absorbency.
Co-pending U.S. patent application Ser. No. 08/877,735 (hereafter "'735 application"), filed Jun. 17, 1997 by L. Mackey et al., discloses and claims wet-like cleansing articles that are especially useful in removing perianal soils. These cleansing articles comprise a substrate material (e.g., a nonwoven) that is treated with a water-in-lipid emulsion. These articles have a number of significant advantages over prior leaning products, especially when in the form of wet-like cleansing articles used to remove perianal soils. These articles release significant quantities of polar liquids (e.g., water) during use for comfortable, more effective cleaning. The continuous lipid phase of the emulsion is sufficiently brittle so as to be easily disrupted by low shear contact (e.g., during the wiping of the skin) to readily release this internal polar phase, but sufficiently tough at elevated temperatures where the lipid is melted to avoid premature release of the polar phase during the rigors of processing. The continuous lipid phase of these articles is also sufficiently stable during storage so as to prevent significant evaporation of the internal polar phase. The normal tensile strength and flushability properties of these articles are not adversely affected when treated with the high internal phase inverse emulsions of the present invention. As a result, users of these articles get comfortable, efficient, moist cleaning without having to change their normal cleaning habits. The application also indicates that the technology is readily useful with other wipes, including wipes for cleaning hard surfaces.
Co-pending U.S. patent application Ser. No. 08/759,589 (hereafter "'589 application"), filed Dec. 5, 1996 by L. Mackey et al. and co-pending U.S. patent application Ser. No. 08/759,547 (hereafter "'547 application"), filed Dec. 5, 1996 by L. Mackey et al., describe wet-like cleaning wipes similar to those described in the '735 application, but which utilize emulsifier systems that provide enhanced fluid retention by the emulsion.
In spite of the significant improvements over prior cleansing articles, the articles described in the '735 application, the '589 application and the '547 application do exhibit some internal phase liquid loss over time, particularly after the articles have been stored at relatively high temperatures (e.g., 125.degree. F.), such as are commonly encountered during shipment and storage in warehouses, trucks, etc. In addition, depending on the nature of substrate utilized, the amount of shear forces applied to the article during use may not be sufficient to release all (or even most) of the entrapped internal phase. To compensate for the level of liquid lost during storage and/or the level of liquid that remains trapped in the emulsion, substrates may necessarily be treated with relatively higher levels of emulsion. If such additional levels are needed, this may negatively impact the processing and economics of the articles.
Accordingly, it would be desirable to provide products for cleaning that offer the benefits provided by the cleansing articles described in the co-pending applications discussed above, but which more efficiently deliver liquid during the wiping process.
Accordingly, it is an object of the present invention to provide nonwoven, preferably paper-based, wiping articles which (i) are initially dry to the touch, but are capable of delivering liquid during the wiping process, (ii) exhibit minimal evaporation of the liquid portion of the article prior to use, (iii) readily and efficiently deliver liquid during the wiping process, and (iv) have sufficient wet strength integrity to withstand the rigors of the wiping process.